Flotation reagent



Patented June 11, 1940 UNITED STATES FLOTATION REAGENT Emil Ott, lilsmere, Del., assignor to Hercules Powder Company, Wilmington, Del., a corpora tion of Delaware No Drawing. Application July 10, 1937, Serial No. 153,064

9 Claims.

This invention relates to a method for the production of a valuable flotation reagent from a by-product of the refining of petroleum, which has heretofore been practically useless.

In therefining of petroleum, more particularly petroleum high in sulfur, it is customary to wash the distillate with an aqueous alkali metal hydroxide solution before or after treating with sulfuric acid, or before sweetening by the use of sodium plumbite. This alkali wash is given in order to eliminate sulfur in the form of sulfuric acid, hydrogen sulfide, various alkyl mercaptans, etc., from the distillate.

This alkaline extract is blown with steam to remove certain sulfur compounds, and allow it to be used for the extraction of further distillates. The organic sulfur compounds separated in this way from the extract consisting of various alkyl mercaptans and sulfides have heretofore been burned to get rid of them, and even in burning have given a troublesome problem in the production of sulfur dioxide.

Now, in accordance with this invention, I have found that I can produce a valuable reagent for use in the concentration of minerals by floatation processes by the treatment of this crude mixture of organic sulfur compounds with a free alkali metal, an alkali metal hydroxide or an alkali metal monoxide and with carbon disulflde. This treatment transforms the mixture of alkyl mercaptans presents to alkyl trithiocarbonates. I am unaware as to the effect of this treatment upon the other ingredients present in the mixture. However, contrary to expectation, such a mixed product is a valuable flotation reagent so the compounds themselves eitherdo not have a deleterious effect on the flotation properties of the mixtures, or are themselves transformed into flotation reagents. Furthermore, the organic sulfides and other impurities which may be present in such mixtures, or their reaction products, do not interfere with the desirable appearance of the product,- and do not detrimentally affect its stability. The latter is surprising, and particularly important, since products of this type have a tendency to instability.

It will be appreciated that by means of my invention I not only provide a valuable flotation reagent from material which has heretofore been substantially useless, but also avoid any complex refining procedures for the separation of the alkyl mercaptans from other materials, such as, sulfides, disulfides, and various complex sulfur compounds which may be present. In this way I provide a very economical and efllcient process for making a valuable flotation reagent.

The crude mixture which I treat contains, along with the complex impurities, methyl mercaptan, propyl mercaptans, butyl mercaptans, 5 ethyl mercaptan, and higher alkyl mercaptans, in smaller amounts, and ordinarily boils within the range of about C. to about 170 C. How- I ever, the boiling range of the mixture used may be more narrow by simple distillation, giving fractions having a higher content of any one component. However, with the exception of the highly volatile methyl mercaptan, it is practically impossible to separate the individual mercaptans as pure compounds from such a complex crude mixture, due to the closeness of the boiling points of the various components.

While methyl mercaptan occurs in such crude mixtures in substantial amounts, it is frequently desirable to reduce its amount in the mixture, 20 due to its pronounced and disagreeable odor. This may be readily accomplished at the refinery by adjustment of the conditions of condensation of the mixture, or by distilling it out of the mixture before reaction to form the 25 trithlocarbonate.

In-carrying out the method in accordance with this invention I prefer to use substantially molecular proportions of alkali metal hydroxide, alkalimetal, or alkali metal monoxide, as the case may be, and carbon disulfide with an amount of the crude mixture which corresponds to the average molecular weight of the alkyl mercaptans present, or an amount of the crude mixture slightly in excessof the average molecular weight of the alkyl mercaptans'present. In any case, it is desirable to carry the reaction to completion so that a minimum of free alkali metal hydroxide or alkali metal remains in the final product, since its presence tends to render the product 40 unstable.

The alkali metal hydroxide which I use may be, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, etc., and may be used either in the form of a solid or in aqueous 5 solution. The alkali metal monoxide which I use may be, for example, sodium monoxide, potassium monoxide, lithium monoxide, etc., and will desirably be used in the form of flakes or a finely divided powder to secure uniform and rapid reaction. When used in solid form, the alkali metal hydroxide will likewise desirably be used in the form of a powder or flakes to secure uniform and rapid reaction. When the alkali metal hydroxide is used in the form of an aqueous solution, the aqueous'solution will desirably contain about 5% by weight to about 50% by weight of the alkali metal hydroxide and preferably about 25% to about 45%.

While, in general, I prefer to use an alkali metal hydroxide or an alkali metal monoxide, and particularly sodium hydroxide or monoxide, in carrying out the method in accordance with this invention, the free alkali metals, such as, for example, sodium, potassium, caesium, etc., may be used. Sodium hydroxide is particularly suitable for the reaction and.- is inexpensive. The alkali metals, however, present disadvantages" in their high cost and in the danger attendant in handling them. When they are used, they will be substituted for equivalent quantities of the monoxide or hydroxides. It will be understood, howeventhat the use of alkali metals, the monoxides and the hydroxides fall within the scope of my invention. It will also be understood. that the products of the reaction of an alkali metal hydroxide, an alkali metal monoxide or a free alkali metal are fully equivalent and are all within the scope of my invention.

-In carrying out this reaction, it is desirable to avoid oxidizing conditions, since the product .is sensitive in this respect, and hence I prefer to exclude any oxygen from the reaction mixture with a non-oxidizing gas, such as, for example, nitrogen, carbon disulflde, alkyl mercaptans, etc., or under vacuum in a closed system.

The temperature at which I carry out this reaction may be within the range of about 0 C. to an upper limit set by the reflux temperature of the volatile ingredients of the reaction mixture. This upper temperature limit will be set by the reflux of the carbon disulflde or by the reflux temperature of the alkyl mercaptan mixture, depending upon which boils at the lower temperature. I prefer to use a temperature within the range of about 0 C. to about 40 C.

In carrying out the method in accordance with this invention the crude alkyl mercaptan mixture, the alkali metal hydroxide and carbon disulflde may be mixed in any desired order in a reaction vessel in which the reactants can be thoroughly mixed and which is provided with a reflux condenser and means for adequate cooling.

Adequate cooling is desirable to prevent loss of the volatile ingredients by evaporation, and avoid thermal decomposition of the product. The reaction vessel will desirably be flooded with inert gas when necessary to avoid oxidation of the product and any tendency to explosion.

When using an aqueous solution of an alkali metal hydroxide for carrying out this reaction, the product may be recovered by precipitation from the reaction mixture, and the mother liquor remaining used as the reaction medium in a subsequent batch for the production of another lot .of the material; thus, avoiding loss of the product due to solution in the mother liquor.

When the alkali metal, alkali metal hydroxide or alkali metal monoxide is used in solid form a EXAMPLE I Twenty-five pounds of flaked sodium hydroxide were placed in a Werner-Pfleiderer type mixer,

Degrees centigrade Initial boiling point 30 10% 33 20% 35 30% 37 40% 39- 50% 42 60% '45 70% 48 54 64 Final boiling point 163 The rate at which the crude mixture of mercaptans was added was controlled so that the temperature was not allowed to exceed about 45 to 50 C. and required about 2 hours. After the addition of the mercaptan mixture was complete, the mixing was continued until the reaction was completed, as indicated by a drop in the temperature. This occurred in about one hour after the addition of the mercaptan. Forty-seven and one-half pounds of carbon disulflde were then slowly added to the mixture, the rate of addition being adjusted so the temperature did not exceed 45 C. to 47 C. This addition required about 3 hours. The mixing was then continued for another 3 hours, at the end of which the temperature had dropped to 30' to 33 C., indicating the completion of the reaction. This product was a solid, and was found to be valuable as a flotation reagent for the concentration of mineral ores without further purification orrefining.

EXAMPLE I! Twenty-five parts by weight of the crude mercaptan mixture described in Example I and 30.5 parts by weight of carbon disulflde was mixed together in a reaction vessel provided with a reflux condenser and stirring thereaction mixture. Sixteen parts by weight of powdered sodium hydroxide was added to the reaction mixture in small portions at short intervals.- The mixture was agitated between each addition of caustic,and a slight refluxing of the mercaptan took place. At the end of the reaction the product, after being cooled to room temperature, was a hard, apparently dry material. It was pulverized with a recovery of 68 parts by weight, and was found to be a valuable flotation reagent.

ExAuPLn III Thirty-seven parts of the crude mixed mercaptans described in Example I, and 43 parts of carbon disulflde were mixed together. Twentytwo and one-half grams of sodium hydroxide in a 40% aqueous solution was then added slowly with stirring. The reaction mixture was cooled to avoid vigorous reflux of the volatile components of the reaction mixture. After the caustic solution had been entirely added, the reaction mixture was a thick, pasty, yellow mass. This mass was then centrifuged and dried to obtain 68 parts by weight of the product which was a valuable flotation reagent.

I EXAMPLE IV Ten parts by weight of an aliphatic mereaptan cut boiling within the range of about 70 C. to about 94 C. secured by the fractionation of a crude mixture of mercaptans obtained as a byproduct of petroleum refining, consisting principally of a mixture of butyl mercaptans with the impurities boiling in this range, and 3.4 parts by weight of sodium monoxide were thoroughly admixed together until all particles of the sodium monoxide were broken up and had disappeared. Then parts by weight of carbon disulfide were then added to the reaction mixture and the stirring continued. Reaction was indicated by a rise in temperature and by the reaction mass turning yellow. At the end of the reaction, as indicated by a drop in temperature, a thick pasty mass remained, which set up to an apparently dry solid on standing. Fourteen parts by weight of the product were recovered, which consisted principally of a mixture of sodium butyl trithiocarbonates, with the impurities either in their original or reacted form.

EXAMPLE V Fourteen parts by weight of a fraction of a crude mixture of aliphatic mercaptans secured as a by-product of the refining of petroleum. boiling within the range of 20 C'. to 40 C. were added slowly with cooling to 3.7 parts by weight of metallic sodium. Twelve parts by weight of carbon disulfide were then added and the mixture thoroughly agitated with suflicient cooling to keep the temperature below the reflux temperature of the mercaptan present. The agitation of the reaction mixture was continued until it ceased to evolve heat. Twenty-four parts by weight of the product, a yellow solid, was recovered. I

The flotation reagent in accordance with this invention is a valuable collector in the froth flotation of ores and is equally or even more efiicient than collectors heretofore prepared from relatively pure reagents. This is surprising to me in view of the heterogeneous composition of the crude mercaptan mixture from which I prepare this new flotation reagent. It may be used in the flotation of many types of ores and finds general application, for example, in the froth flotation of metallic sulfide ores for the concentration of lead, copper, zinc, gold, silver, etc.

While this reagent has great selective action or collecting action in the froth flotation of sulfide minerals in the flotation operation, it does not have substantial frothing properties, so that an appropriate frothing agent, such as pine oil, should be employed in conjunction therewith in carrying out the flotation operation. In carrying out the flotation operation, it is preferable to use either an alkaline or a neutral circuit depending upon the character of the ore. In an acid circuit the various alkyl trithiocarbonate salts contained in this reagent have a tendency to instability, depending upon the acidity of the circuit and the particular compound. A slightly acid circuit can be successfully used, however, if sufficient reagent is added to compensate for whatever loss may occur due to decomposition during the flotation operation.

The amount of the flotation reagent in accordance with this invention, which will be used in froth flotation will depend upon the particular ore being treated. Ordinarily, it will be found that the optimum amount will be within the range of about 0.02 lb. to about 0.7 lb. per ton of dry ore feed, and usually within the range of about 0.05 lb. to about 0.5 lb. per ton of dry' low EXAMPLE VI Matahambre copper ore from Santa Lucia, Cuba, containing chalcopyrite and pyrite in a shale gangue and analyzing 4.7% copper, 17.8% iron and 46.8% insoluble matter was tested in a copper circuit as follows: It was prepared in a 50% pulp in water by crushing 1015 grams of the ore to pass 8 mesh, admixing with an equal weight of tap water and then grinding'in a ball mill to a fineness of greater than 48 mesh. Two thousand grams of this pulp were then transferred to a 1000 gm. Denver Sub-A Fahrenwald type flotation machine impeller speed 1800 R. P. M., and further diluted to 20% solids. To this diluted pulp was then added per ton of dry ore 0.12 lb. of the flotation reagent described in Example I, above, 0.08 lb. of sodium cyanide, 1.0 lb. of lime and 0.56 lb. of pine oil and the mixture was then frothed for 10 minutes, yielding a concentrate and tailing as shown in Table I in comparison with the heads.

Table I Percent Cu percent Cu percent I weight assay distribution To obtain a comparison with current plant practice, using a well known and widely used flotation reagent the above procedure was repeated, with the substitution of pentasol xanthate for the flotation reagent made in accordance with this invention. Using pentasol xanthate as the flotation reagent, the following results were obtained:

Table II Percent Cu percent Cu percent weight assay distribution Concentrate 10. 7 22. 7 92. 0 Telling 80. 3 0. 48 8. 0 Heads 100. 0 5. 100. 0

EXAMPLE VII Asample of St. Joseph Balmat zinc ore, from Balmat, N. Y., which is a mixture of metallic sulfides of lead, zinc and iron (galena, sphaleritemaramatitc, pyrite) vm a siliceous-dolomitic gangue, and which analyzed 0.23% Pb, 8.3 Zn, 17.4% Fe and 30.3% insolubles, was subjected to froth flotation in a zinc circuit by the following procedure: .One thousand and six grams of this ore were crushed to pass 8 mesh, admixed with an equal Weight of tap water and then ground in a ball mill to a fineness of minus 48 mesh. Two thousand grams of the resulting minus 48 mesh pulp was then transferred to a 1000 g. Denver Sub-A Fahrenwald type flotation machine (impeller speed 1800 R. P. M.), and further diluted to 20% solids. To this pulp was then added per ton of dry ore 0.06 lb. of sodium cyanide, 2.00 lbs. of lime and 1.4 ibs .-of copper sulfate, and the pulp conditioned by agitation for ten minutes. After the conditioning was completed 0.10 lb. of the flotation reagent prepared by the procedure of Example I and 0.15 lb. of pine oil was added. F'rothing for 10 minutes yielded the concentrate and tailing as shown in Table III.

Table III Zn percent distribution Percent Zn percent weight assay Concentrate V 15. 46. 5 'Iails 1. 84. 0. 76 Heads 100. 7. 80

To secure a comparison approximating plant practice for this ore, the above procedure was repeated with the substitution of 0.10 lb; of potassium ethyl xanthate for the flotation reagent made in accordance with this invention, with the A comparison of the data of Tables III and IV shows that the flotation reagent in accordance with this invention collected a concentrate containing a higher percentage of zinc than the ethyl xanthate did, and thereby is a more emcient collector than ethyl xanthate in the flotation of zinc ores.

EXAMPLE VIII St. Joseph Edward's ore, from Edwards, N. Y., is similar to the Balmat concentrated in Example VII in being a massive sulfide with substantially the same gangue minerals but without alteration products. The zinc therein occurs as sphalerite ZnS. A sample of this ore which analyzed 11.8% Zn, 8.0% Fe, 16.1% CaO and 3.1% insolubles was prepared as a pulp containing 50% solids following the same procedure described in Example VII, except that the ore was ground to a minus mesh. Two thousand grams of this pulp were then placed in a 1000 gram Denver Sub-A Fahrenwald type flotation machine and further diluted to 20% solids. This pulp was then conditioned by ten minutes agitation after the addition per ton of dry ore of 5.5 lbs, of lime and '1 .4'lbs. of copper sulfate, after which 0.16 lb. of the flotation reagent prepared by the procedure of Example I and 0.22 lb. of pine oil were added. Frothing for ten minutes Table V.

For comparison approximating plant practice on this ore, the above procedure was repeated using 0.16 lb. of potassium ethyl xanthate instead of the same amount of the flotation reagent made. in accordance with this invention, with the results shown in Table VI.

Table VI Percent Zn percent Zn percent weight assay distribution Concentrate 25. 5 48. t 96. 0 Tails. 74. 5 0. 71 4. 0 Heads 100. 0 12. 9 100. 0

A comparison of the data of Tables V and VI shows that again the flotation reagent in accordance with this invention gave a concentrate containing a higher percentage of zinc than that obtained using potassium ethyl xanthate.

EXAMPLE IX Midvale lead ore from Midvale, Utah, is a high grade sulfide ore containing lead as galena, zinc as sphalerite and iron as pyrite and analyzes 17.8% Pb, 9.1% Zn, 10.8% Fe, and 31.4% insolubles. A sample of this ore was subjected to flotation in a zinc circuit by the following procedure:

' One thousand grams of this ore were made into a pulp with tap water, ground to a fineness of minus 48 mesh and placed in the flotation machine and diluted to 20% solids, as in the preceding examples. To this pulp was then added per ton of dry ore 0.40 lb. of the flotation reagent prepared by the procedure described in Example I, 1.0 lb. of zinc sulphate, 1.0 lb. of sodium sulphate, 0.43 lb, of coal tar creosote and 0;l9 lb. of pine oil. The pulp was then frothed for 10 minutes yielding the concentrate and tailing as shown in Table VII.-

Table VI! Percent Pb percent Pb percent weight assay distribution To obtain a comparison approximating plant procedure for this ore the above test was duplicated with the substitution of 0.40 lb. of potassium ethyl zanthate for the flotation reagent of this invention. The results given in Table VIII were obtained:

A comparison of the data of Tables VII and VIII shows the flotation reagent in accordance with this invention to be more eflicient than the widely used potassium ethyl xanthate for the.

- monoxide, alkali metals and with flotation of lead ores. Thus, it will be observed that both the percentage of lead in the concentrate (Pb per cent assay) and the per cent of total lead recovered in the concentrate (Pb per cent distribution) was higher when my new flotation reagent was used than when potassium ethyl zanthate was used.

It will be understood that the details and ex-- amples hereinbefore set forth are illustrative only, and that the invention as herein broadly described .and claimed is in no way limited thereby.

What I claim and desire to protect by Letters Patent is:

1. A flotation reagent consisting of the reaction product of an alkali metal hydroxide, carbon disulfide and a crude mixture of organic sulfur compounds rich in alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds, said crude mixture being that by-product of petroleum refining obtained by steam blowing the extract resulting from the treatment of petroleum in an aqueous alkali solution, the said reaction product comprising a mixture of alkali metal mono-alkyl trithiocarbonates, and other organic sulfur compounds.

2. A method for the production of a flotation reagent from that by-product of petroleum refining obtained by steam blowing the extract resulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds which comprises reacting the crude v mixture with a material from the group consisting of alkali metal hydroxide,.alkali metal 3. A method for the production of a flotation reagent from that by-product of petroleum refining obtained by steam blowing the extract re-' sulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds which comprises reacting the crude mixture withalkali metal hydroxide and with carbon disulfide.

4. A method for the production of a flotation reagent from that by-product of petroleum refining obtained by steam blowing the extract resulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur com- 60 pounds which comprises reacting the crude mixcarbon ture with an aqueous solution of alkali metal hydroxide and with carbon disulfide.

. 5. A method for the production of a flotation reagent from that by-product of petroleum refining obtained bysteam blowing the extract resulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds which comprises reacting the crude mixture with solid alkali metal hydroxide and with carbon disulfide.

6. A method for the production of a flotation reagent from that by-product of petroleum refining obtained by steam blowing the extract resulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds which comprises reacting the crude mixture with an alkali metal hydroxide and then with carbon disulfide.

7. A method for the production of a flotation reagent from that by-product of petroleum refining obtained by steam blowing the extract resulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds, which comprises reacting the crude mixture with sodium hydroxide and with carbon disulfide.

9. A method for the production of a flotation reagent from that by-product of petroleum reflning obtained by steam blowing the extract resulting from the treatment of the petroleum in an aqueous alkali solution and which consists of a crude mixture of organic sulfur compounds rich in lower alkyl mercaptans but containing a minor amount of non-mercaptan organic sulfur compounds which comprises reacting thecrude mixture with an alkali metal hydroxide and with carbon disulfide under substantially non-oxidizing conditions. 

